The present invention relates to a flameproof thermoplastic resin composition. More particularly, the present invention relates to a flameproof thermoplastic resin composition that comprises a rubber modified styrene-containing resin and a polyphenylene ether resin as a base resin, a styrene-acrylonitrile copolymer containing from 5 to 18% by weight of acrylonitrile as a compatibilizer, an aromatic phosphoric acid ester compound with a melting point of above 90xc2x0 C. as a main flame retardant, and a phenolic resin as a further flame retardant.
A rubber modified styrene-containing resin has a good processability, a high impact strength, and a good appearance. Accordingly, the resin has been widely applied to electric appliances and office supplies. In case that a rubber modified styrene-containing resin is applied to personal computers, facsimiles, and the like, which emit heat, flame-retardant property should be given to the resin due to a combustibility. A widely known method for the flame retardancy is that halogen-containing compounds or antimony-containing compounds are added to a rubber modified styrene-containing resin to give flame-retardant property. The halogen-containing compounds used in above method are, for example, polybromodiphenyl ether, tetrabromobisphenol A, epoxy compounds substituted by bromine, chlorinated polyethylene, etc. An antimony trioxide and an antimony pentaoxide are commonly used as antimony-containing compounds.
The methods for improvement of flame-retardant property by applying halogen- and antimony-containing compound have advantages such as easy acquirement of the flame-retardant property and no degradation of the physical properties. However, the disadvantages could be observed that the halogen-containing compound results in the corrosion of the mold itself by the hydrogen halide gases released during the molding process and is fatally harmful due to the toxic gases liberated in case of fire. Especially, since a polybromodiphenyl ether, mainly used for a halogen-containing flame retardant, can produce toxic gases such as dioxin or furan during combustion, flame retardants which are not prepared with halogen-containing compound have become main concerns in this field.
It is commonly known a method to apply phosphorus or nitrogen compounds as halogen-free flame retardant to a resin composition. However, usage of only phosphorus compound deteriorates heat resistance of a rubber modified styrene-containing resin and does not impart sufficient flame retardancy.
Generally, when a rubber modified styrene-containing resin such as ABS is burned, a char is not produced due to decomposition and vaporization in most parts (Journal of Applied Polymer Science, 1998, vol 68, p1067). Therefore, to impart an effect of flame retardancy, it is necessary to add a char-forming agent to a resin composition, which plays a role to prohibit entrance of oxygen and emission of fuel by forming char on the surface of rubber with three-dimensional carbon chain bonds under combustion.
Japanese Patent Laid-open No. 7-48491 discloses a flameproof thermoplastic resin, made of adding a novolac phenolic resin and a phosphoric acid ester into a thermoplastic copolymer resin composed of a rubber copolymer and an aromatic vinyl monomer. It was found that in order to obtain a good property of flame retardancy, a phenolic resin as a char-forming agent and a phosphoric acid ester compound as a flame retardant should be added in a lot of amount. However, in this case, the heat resistance of the resin composition is dropped suddenly.
The present inventors have made it possible to prepare a flameproof resin composition by mixing a styrene-acrylonitrile copolymer having from 5 to 18% by weight of acrylonitrile as a compatibilizer, an aromatic phosphoric acid ester compound as a main flame-retardant and a phenolic resin as a further flame-retardant to improve flame-retardant property of a resin composition and adding the mixture to a base resin comprising a rubber-modified styrene-containing resin and a polyphenylene ether resin. Therefore, good mechanical properties as well as a good improvement of flame retardancy and heat resistance have been obtained.
An object of the present invention is to provide a thermoplastic resin composition which has a good property of flame retardancy.
Another object of the present invention is to provide a flameproof thermoplastic resin composition which has a good characteristic of heat resistance.
A further object of the present invention is to provide a flameproof thermoplastic resin composition which has good mechanical properties.
A further object of the present invention is to provide a flameproof thermoplastic resin composition which does not contain halogen-containing compounds which causes the environmental pollution during the preparation or combustion of the resin.
Other objects and advantages of this invention will be apparent from the ensuing disclosure and appended claims.
A flameproof thermoplastic resin composition of the present invention comprises (A) a base resin comprising 40 to 95% by weight of a rubber modified styrene-containing resin (a1) composed of 20 to 100% by weight of a styrene-containing graft copolymer resin (a11) and 0 to 80% by weight of a styrene-containing copolymer resin (a12), and 60 to 5% by weight of polyphenylene ether resin (a2); (B) 2 to 40 parts by weight of a styrene-acrylonitrile copolymer containing 5 to 18% by weight of acrylonitrile per 100 parts by weight of the base resin; (C) 5 to 30 parts by weight of an aromatic phosphoric acid ester compound having a melting point of more than 90xc2x0 C. per 100 parts by weight of the base resin; and (D) 3 to 30 parts by weight of a phenolic resin per 100 parts by weight of the base resin. The flameproof thermoplastic resin composition may further comprise 0 to 30 parts by weight of an anti-dripping agent, an impact modifier, a plasticizer, a heat stabilizer, an oxidation inhibitor, a light stabilizer, a compatibilizer, pigments, dyes and/or inorganic fillers on the basis of 100 parts by weight of the base resin.